1. Field of the Invention
The present invention relates to a projection type display for application to a projector that projects, for example, color video images onto a screen, and more particularly, to the improvement in uniformity of video images projected onto a screen.
2. Description of the Background Art
Conventionally, there is known a projection type display that modulates and composes illumination light beams generated by light sources based on image signals and projects those onto a screen, to thereby display video images on the screen. With increasing demands for downsizing and lower power consumption of a device and a longer life of a light source, nowadays, light emitting diodes (LEDs) have been widely used as light sources in place of conventional discharge lamps. For example, the illumination light beams from light sources composed of three LEDs respectively emitting light beams of three primary colors, red, green, and blue, are composed by a dichroic mirror, dichroic prism, or the like, and then modulated into video light by an image display device such as a digital micromirror device (DMD), whereby a color video image is projected.
The LEDs used in the projection type display as described above are classified into one type in which a light emitting part is formed of one LED and the other type in which a light emitting part is formed of an LED array including a plurality of LEDs arranged therein. In the case of the LED array, each LED array is divided into a plurality of groups, and a drive circuit is provided per group.
For example, in a case where one LED array is formed of six LEDs, a drive circuit is provided for each of the two groups each including three LEDs, or a drive circuit is provided for each of the six groups each including one LED. Driving of an LED is controlled per group, which enables to individually turn on or turn off three or one LED among the six LEDs.
The illumination light beams emitted from three LEDs respectively emitting red, green, and blue light beams or an LED array are composed from three different optical paths into one optical path by a dichroic mirror or a dichroic prism, and then radiated on an image display device such as a DMD through an integration device. The integration device is, for example, a well-known light tunnel or glass rod. The illumination light passes through the integration device while being reflected thereon, which uniformizes the illuminance distribution of the illumination light. The illuminance distribution differs depending on an entrance position of an illumination light beam on an integration device, and thus, the illuminance distributions of the respective colors do not coincide with each other, causing uneven chromaticity.
For example, Japanese Patent Application Laid-Open No. 2007-322792 proposes a device in which, in order to reduce uneven chromaticity, each of a plurality of light source units is provided with an adjustment mechanism so as to move in parallel with a direction perpendicular to the optical axis thereof, to thereby adjust the illumination light beams of the respective colors emitted from the light source units to positions with an optimum illuminance distribution with respect to a wavelength shift caused by the incident angle dependence of a cross dichroic mirror constituting a color composing unit.
In a case where LED arrays each composed of a plurality of LEDs are used as a light source in the device described in Japanese Patent Application Laid-Open No. 2007-322792, no problem arises when all the LEDs in the LED arrays are turned on. However, if LEDs to be turned off are randomly selected per LED array in a case where part of the LEDs constituting the LED array is turned off, by merely adjusting the position of the entire light source units, overlaps of the light source images do not coincide with each other when the illumination light beams respectively emitted from the LED arrays are composed. This tends to generate uneven brightness and uneven chromaticity in video images projected onto a screen.